feat: implement offline workspace integrity and recovery center

[vraj826]

Fixes issue #175

Fixes this issue

This PR introduces a lightweight Offline Workspace Integrity & Recovery Center for DevShell to improve workspace recovery safety, integrity visibility, portability, and recovery diagnostics while preserving the existing filesystem-first architecture.

It addresses:

• missing workspace integrity visibility
• lack of snapshot preview before restore
• no export/import portability flow
• fragmented recovery diagnostics
• weak corruption/recovery awareness

Changes made

• Added workspace integrity validation and recovery warnings
• Added snapshot preview metadata before restore
• Implemented workspace export/import support using existing JSON structures
• Added corruption-aware recovery diagnostics using existing .corrupted infrastructure
• Centralized recovery diagnostics visibility across workspace/replay flows
• Added lightweight integrity/recovery UI panels and warnings
• Added safe validation for malformed imports and invalid snapshots
• Preserved filesystem-only persistence and Electron compatibility

Testing and validation

Tested:

• workspace preview and restore flows
• export/import workflows
• malformed JSON import handling
• integrity warning rendering
• corruption-aware recovery diagnostics
• replay/workspace recovery integration

Validation:

• git diff --check passed
• python -m py_compile app.py passed
• node --check ui/app.js passed

Screenshots and logs

Screen.Recording.2026-05-31.205947.mp4

Checklist

• No breaking changes
• Tests added or updated
• Documentation added or updated
• Branch is up to date with main

[vraj826]

@siddu-k I have done the implementation, can you review the changes!